1. Field of the Invention
The present invention relates generally to the field of lead-acid batteries, and more particularly, to a unique, high performance per unit weight cast-on strap. The strap permits design modifications in battery preparation, such as alteration in plate size, plate count and the potential for elimination of costly and heavy plates from battery plate stacks. More specifically, the present invention relates to the field of cast-on straps which have a low profile and which are highly efficient in transferring current to another caston strap in another cell of the battery.
2. Description of Prior Battery Systems
Lead-acid batteries typically comprise a series of thin, flat, generally rectangular grids for carrying a current through the battery. The grids also serve as a substrate for supporting electrochemically active materials or "paste" added thereto during manufacture to form battery plates. Paste typically comprises a mixture of lead oxide in a dilute acid solution, for example sulfuric acid. The paste composition is determined by power requirements, cost and the battery environment, as is generally known in the art.
It is also known that groupings of individual battery plates may be assembled, interleaved with separator material and electrically connected to form plate stacks. The latter are then assembled in a container to form a final battery. A typical example would be an automobile battery of the 12-volt variety, where six individual stacks are placed into a plastic container having six compartments. To permit current to flow throughout the battery, it is necessary to join the straps of one stack with the appropriate strap of an adjacent stack. Moreover, it is necessary to provide terminal electrodes which will extend through the cover to permit electrical contact with the vehicle's electrical system.
After the battery plates are fully assembled, they are formed, i.e. charged, and the battery is placed into service. An important characteristic of batteries is called "cold cranking power," i.e. the amount of power which can be generated per unit of time. Further reference will be made to cold cranking power in later sections of this specification.
The parent application describes in detail certain prior art relating to the construction of the grids themselves, including the use of screen-like patterns having a plurality of holes into which the porous chemical paste is applied, cured, etc. The parent application also describes the typical offset current collecting lugs extending from each plate, which lugs are eventually coupled by the cast-on straps to complete the electrical circuit. Most commonly, cast-on straps are formed by taking assembled battery plate stacks, inverting them, and dipping the lugs of the stack into molten lead contained within a mold. In the most common batteries in use at the time of the filing of this specification, cast-on straps have an upstanding end portion, as will be explained later and more fully when the drawings are described later herein. The upstanding portion of such cast-on straps have come to be known as the "tombstone" of the straps.
In the parent application, a considerable portion of the specification was devoted to a discussion of grid design which will not be repeated in this application. However, such discussion is expressly incorporated herein by this reference. Moreover, several patents showing cast-on straps or burned-on straps having designs different than the typical tombstone design are within the art and will be described here. For example, in commonly owned U.S. Pat. No. 5,149,605, issued Sep. 22, 1992, Dougherty describes a cast-on strap which is used with a novel dual lug battery plate design, the straps including a pair of spaced apart elongate portions extending in one plane and a laterally extending portion extending in a plane perpendicular to that of the elongate portions. The laterally extending portions, in the Dougherty patent, couple the two elongate portions joining rows of lugs of like polarity.
A different type of strap construction is described in U.K. Patent Application No. 2170348A, published Jul. 30, 1986. This application is entitled, "Storage Battery", and the subject matter thereof was invented by Shiga, et al. The strap of this patent is used with battery plates of conventional design, i.e. those having current collector lugs adjacent the corners of the plates, and the straps include a horizontal base portion and an "ear" portion extending from the horizontal base portion and facing a perforation hole in the wall between plate stacks. The design is for burned-on straps and is said to reduce the height of the conductor or the lugs of the negative or positive plates.
While it is apparent from the foregoing description that numerous plate and grid designs have been developed in the lead-acid battery art, problems still remain in the design and manufacture of such batteries. One of the most significant is the weight associated with this type of energy source. Commercial battery plates include lead alloy grid materials, combined with lead paste materials and the electrolyte. Any system which would reduce the battery weight, while maintaining the power required for a particular application, would be a significant advance in the art.
Further problems relate to the actual manufacture of the batteries, where the plates must be electrically coupled by the cast-on straps and where the straps must be welded to one another in adjacent cells to permit current to flow through the system. Ways in which such current transfer could be increased in efficiency would also represent significant advances.
Furthermore, it is always advantageous to seek ways to maximize the efficiency of the grid-strap current transfer and improvements in this area would also be important.
Any system which would combine solutions to the foregoing problems would represent a further very substantial advance in this technology.